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NIOSH Response to SC&A Review of 

RPRT-0070 Methods for Th-232 Dose 

Reconstructions

Response Paper 

National Institute for Occupational Safety and Health 

December 17, 2018

Mike Mahathy 

Oak Ridge Associated Universities Team

Reviewed by Timothy Taulbee

Division of Compensation Analysis and Support

This is a working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in discussions 

with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or 

ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution. 
Response Paper NIOSH Response to SC&A Review of RPRT-0070 Methods 

for Th-232 Dose Reconstructions

December 17, 2018

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This is a working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in discussions 

with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or 

ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution. 

INTRODUCTION

In 2017, the ORAU Team issued ORAUT-RPRT-0070, Evaluation of Method for Assessment of 

Thorium-232 Exposures at the Savannah River Site from 1972 to 1989 (ORAUT 2017). This is 

an assessment of methods to bound thorium doses at Savannah River Site (SRS) from 1972 

through 1989. In response to ORAUT 2017, SC&A issued SC&A Review of RPRT-0070 

Methods for Th-232 Dose Reconstruction (SC&A 2018). In this document, the ORAU Team 

responds to four observations and one finding recorded by SC&A in their review of ORAUTRPRT-0070 methods 

NIOSH RESPONSES TO SC&A COMMENTS

SC&A Observation 1: The methods used in selecting an appropriate sample size for analysis 

were based on air sampling data from a separate facility during a separate timeframe. NIOSH 

should provide a discussion in RPRT-0070 to demonstrate that the statistical analysis of gross 

alpha air sampling in Building 235-F during the 1970s is sufficiently analogous of the conditions 

in the 773-A Laboratory Areas during the 1980s to justify its use in defining a random sample 

size for exposure potential analysis to thorium (1981–1989).

NIOSH Response: Air monitoring data from 235-F were only used to model the minimum 

number of results needed to provide acceptable confidence in the determination that the limit was 

considered bounding. The model gave the number of air samples needed per year as 750. As 

discussed in Section 3.2 and Figure 3-1 of ORAUT-RPRT-0070, this number was determined by 

visually identifying the point on all of the plots, using the top x-axis (number of results), at 

which there is little change in the sample median (ORAUT 2017). Figure 1 below provides 

Figure 3-1 from ORAUT 2017 for the reader’s convenience. The same air monitoring 

procedures and techniques used in 773-A were used in 235-F and both sampled for gross alpha 

contamination. Air concentration data from 235-F were not used to represent air contamination 

in Building 773-A or to serve as surrogate for Building 773-A.
Response Paper NIOSH Response to SC&A Review of RPRT-0070 Methods 

for Th-232 Dose Reconstructions

December 17, 2018

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This is a working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in discussions 

with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or 

ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution. 

Source: ORAUT 2017, Figure 3-1 

Figure 1. Fraction of Sample Results Expected Over the Censoring Level (censoring level 

for this dataset = 0.1 DAC). 
Response Paper NIOSH Response to SC&A Review of RPRT-0070 Methods 

for Th-232 Dose Reconstructions

December 17, 2018

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This is a working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in discussions 

with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or 

ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution. 

SC&A Observation 2: Because the air sampling methodology only applies to the period after 

May 1980 (or alternately December 1980), it is not clear why NIOSH chose to analyze air 

sampling data during the year 1975 as shown in Figure 3-2 of RPRT-0070. Inclusion of such 

data is likely inappropriate.

NIOSH Response: Given that this approach is limited to the time period of 1980 through 1989, 

NIOSH agrees that 1975 should not have been included in the analysis. However, given that the 

limiting air concentration was the censoring level for all years, the exclusion of 1975 does not 

impact this methodology. 

SC&A Observation 3: Given that the cited air sample references only report the values that 

were above the CL (1×10-12 μCi/cm3), SC&A requests clarification of how the total number of 

samples (i.e., the denominator) was determined as presented in Figure 3-2 of RPRT-0070.

NIOSH Response: As discussed above in the response to Observation 1, NIOSH performed an 

analysis of the 773-A laboratory areas during the 1980s in order to define a random number of 

samples needed (ORAUT 2017). The assumption was made that the sampling program across 

the SRS site during the 1980s would be consistent in its implementation. Therefore, a known 

dataset could be used to determine the number of random samples needed to estimate the true 

number of samples that were above the censoring level. This number was determined to be 750 

samples. To collect a random set of sample results, a list of random days for each year to be 

sampled was created. The air sample results were compiled for each random day on the list until 

a total of at least 750 random sample results were compiled. If the 750th random sample result 

was compiled in the middle of the random day, all sample results for that day were included. 

This resulted in 795 results analyzed for 1975, 817 results analyzed for 1981, 753 results 

analyzed for 1984, and 750 results analyzed for 1987. 

SC&A Observation 4: Based on SC&A’s analysis of the relative magnitude and location of 

positive air sampling results, SC&A agrees that the use of the CL of 1×10-12 μCi/cm3 over the 

course of an entire year represents a reasonable upper bound on the exposure potential to 

thorium under normal conditions associated with storage and material transfer activities.

NIOSH Response: No response needed.
Response Paper NIOSH Response to SC&A Review of RPRT-0070 Methods 

for Th-232 Dose Reconstructions

December 17, 2018

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This is a working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in discussions 

with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or 

ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution. 

SC&A Finding 1: Per the hierarchy of data criteria, bioassay sampling is considered 

scientifically preferable to other data and methods, such as the use of air sampling and/or 

modeling assumptions based on source term inventories. While alternate methods other than the 

use of bioassay monitoring may be useful in situations where exposure potential is essentially 

routine or ambient in the facility, such methods may not be applicable to workers involved in 

off-normal conditions, such as direct maintenance, modification of previously contaminated 

equipment, or other D&D activities.

NIOSH Response: NIOSH agrees that, given the type of air data collected, the intake rate 

associated with these data should only be used for normal conditions. For off-normal conditions 

(e.g., direct maintenance, modification of previously-contaminated equipment, or other D&D 

activities), the use of the 50th percentile co-worker intake can be used to bound exposure; given 

the nature of this type of work, this approach would only apply to construction trade workers. 

The co-worker intake should be limited to the 50th percentile because there is no indication that 

these types of activities would result in air concentrations associated with the 95th percentile. 

The 95th percentile co-worker intake rates are based on a time period when thorium operations 

were being performed and trivalent radionuclide bioassay was being used (which would have 

captured additional radionuclides, thus biasing the co-worker intake high). NIOSH concludes

that the 50th percentile would sufficiently bound any exposures associated with off-normal 

conditions for construction trade workers. 

REFERENCES

ORAUT (Oak Ridge Associated Universities) 2017, Evaluation of Method for Assessment of 

Thorium-232 Exposures at the Savannah River Site from 1972 to 1989, ORAUT-RPRT-0070, 

May 15. SRDB Ref ID: 166846 

SC&A (SC&A, Inc.) 2018, Memorandum: SC&A Review of RPRT-0070 Methods for Th-232 

Dose Reconstruction, October 11. SRDB Ref ID: 175229